First cut of a basic calculator UI example.

guecs.cpp

@@ -220,4 +220,9 @@ namespace guecs {
       set<Label>(ent, to_set);
     }
   }
+
+  wstring to_wstring(const string& str) {
+    std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> $converter;
+    return $converter.from_bytes(str);
+  }
 }